Position detecting apparatus having electric motor and method for detecting position

ABSTRACT

A reference position detecting apparatus includes an electric motor and a motor control unit. The electric motor includes a plurality of first coils and a plurality of second coils. The electric motor further includes a rotor that rotates when at least one of the plurality of first coils and the plurality of second coils is supplied with electricity. The motor control unit controls electricity supplied to either one of the plurality of first coils and the plurality of second coils to rotate the rotor to a limit position in a movable range of an object.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a division of application Ser. No. 11/318,529 filedDec. 28, 2005, which is in turn based on Japanese Patent Application No.2004-381753 filed on Dec. 28, 2004, the disclosure of which isincorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a position detecting apparatus havingan electric motor. In particular, the present invention relates to anapparatus for detecting a reference position of a driven object todefine an initial position of the driven object in a starting conditionof a vehicle. Specifically, the present invention relates to atechnology for defining an initial position of one of a rotor and ashift range switching device using an electric motor in an automatictransmission apparatus for a vehicle, for example. In addition, thepresent invention relates to a method for detecting a position in anobject.

BACKGROUND OF THE INVENTION

According to JP-A-2004-12299 (U.S. Pat. No. 6,911,798 B2), an electricmotor operates a shift range switching device for an automatictransmission of a vehicle. In this structure, an electric motor issupplied with electricity to perform a tapping control, when a referenceposition of a rotor or a shift position is unknown in a startingcondition of the vehicle. During the tapping control, the rotor isrotated to a limit position on one side in a movable range of the shiftrange switching device, for example, so that the rotor is rotated untilthe rotor reaches at the limit position. The limit position is on theside of the parking position, for example. The position, in which therotor stops, is defined as one of the reference position in the rotationcontrol of the rotor and a reference position of the shift switchingcontrol, during the tapping control.

When the tapping control is performed, the following problems may arise.First, when a movable member collides against a fixed member in thetapping control, a mechanical load is applied to both the movable memberand the fixed member. Alternatively, when the movable member is stoppedwhile an electric motor is supplied with electricity, load torque isapplied to components in both a transmission system for rotating themovable member and a hooking portion, in which the movable member hooksto the fixed member, due to torque applied by the electric motor.Accordingly, as the number of the tapping control increases, mechanicaldamage may occur in the components of the transmission system and in thehooking portion, in which the movable member hooks to the fixed member.As a result, the components of the transmission system and the hookingportion may be gradually deformed and broken.

Second, output voltage and a capacity of a power source such as abattery may vary in dependence upon the environment such as atmospherictemperature and an operating condition. In this case, electricitysupplied to the electric motor from the power source may vary, andoutput torque of the electric motor may change. Specifically, the outputtorque of the motor may increase in dependence upon the environment andthe operating condition. In this situation, mechanical load may increasewhen the movable member collides against the fixed member.Alternatively, large mechanical torque may be applied to the componentsin the transmission system and the hooking portion, because of supplyingelectricity to the electric motor even when the movable member stops.Accordingly, as the number of the tapping control increases, the numberof applying large load torque increases, and as a result, mechanicaldamage may occur in the components of the transmission system and thehooking portion.

In addition, the components are not necessarily perfect rigid bodies.That is, the components are macroscopically spring elements, and thecomponents may cause deflection when being applied with force. Whenoutput torque of the motor varies, an amount of deflection arising inthe components varies. As a result, the reference position, which islearned during the tapping control of the movable member, cannot bestable. Thus, a positioning control of the movable member cannot besteadily performed.

Third, as the rotation speed of the electric motor increases, the outputtorque of the electric motor decreases. By contrast, as the rotationspeed of the electric motor decreases, the output torque of the electricmotor increases. Accordingly, when the movable member stops while theelectric motor is supplied with electricity, the electric motorgenerates the maximum torque. Consequently, large mechanical torque isapplied to the components of the transmission system and the hookingportion between the movable member and the fixed member. Accordingly, asthe number of the tapping control increases, the number of applyinglarge load torque increases. Consequently, mechanical damage may occurin the components of the transmission system and the hooking portion.

SUMMARY OF THE INVENTION

In view of the foregoing and other problems, it is an object of thepresent invention to produce a position detecting apparatus, theapparatus being capable of reducing damage occurring in a detectingoperation of the position. It is another object of the present inventionto produce a method for detecting the position in an object.

According to one aspect of the present invention, a reference positiondetecting apparatus includes an electric motor, a driven object, atapping control unit, and a reference position recognizing unit. Theelectric motor includes a coil device and a rotor. The rotor rotateswhen the coil device is supplied with electricity. The driven object isdriven by the rotating rotor. The tapping control unit performs atapping control, in which the rotor rotates to a limit position on oneside in a movable range of the driven object. The reference positionrecognizing unit defines a point, at which rotation of the rotor stops,as a reference position of one of the rotor and the driven object duringthe tapping control.

The coil device may have a first coil group and a second coil group. Thefirst coil group includes a plurality of first coils, which electricallyconnect with each other. The second coil group includes a plurality ofsecond coils, which electrically connect with each other. The first coilgroup including the plurality of first coils is electrically separatedfrom the second coil group including the plurality of second coils. Thetapping control unit may control electricity supplied to either one ofthe first coil group and the second coil group to rotate the rotorduring the tapping control.

The tapping control unit may perform a duty control with respect toelectricity supplied to the either one of the first coil group and thesecond coil group such that an amount of electricity flowing through theeither one of the first coil group and the second coil group becomessubstantially constant during the tapping control.

The tapping control unit may perform a duty control with respect toelectricity supplied to the either one of the first coil group and thesecond coil group in accordance with speed of the rotor such that anoutput torque of the rotor becomes substantially constant during thetapping control.

A method for detecting a position in an object, the method includes thefollowing step. Electricity supplied to either one of a plurality offirst coils and a plurality of second coils in an electric motor iscontrolled to rotate a rotor to a limit position in a movable range ofthe object.

A duty control may be performed with respect to electricity supplied tothe either one of the plurality of first coils and the plurality ofsecond coils such that an amount of electricity flowing through theeither one of the plurality of first coils and the plurality of secondcoils becomes substantially constant.

A duty control may be performed with respect to electricity supplied tothe either one of the plurality of first coils and the plurality ofsecond coils in accordance with speed of the rotor such that outputtorque of the rotor becomes substantially constant.

In the above structure, a load caused by collision of components can bereduced. Therefore, mechanical damage in the components can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will become more apparent from the following detaileddescription made with reference to the accompanying drawings. In thedrawings:

FIG. 1A is a schematic view showing an electric motor, and

FIG. 1B is a graph showing a relationship between rotor angle and anenergizing condition of a coil, according to a first embodiment of thepresent invention;

FIG. 2 is a partially cross sectional side view showing a shift rangeswitching device according to the first embodiment;

FIG. 3 is a schematic diagram showing a system of the shift rangeswitching device according to the first embodiment;

FIG. 4 is a perspective view showing the shift range switching deviceaccording to the first embodiment;

FIG. 5 is a schematic view showing an electric motor according to thefirst embodiment;

FIG. 6 is a schematic diagram showing an electric connection of theelectric motor, according to the first embodiment;

FIG. 7 is a perspective front view showing a reduction gear according tothe first embodiment;

FIG. 8 is a perspective rear view showing the reduction gear accordingto the first embodiment;

FIG. 9 is an exploded perspective view showing the reduction gearaccording to the first embodiment;

FIG. 10A is a front view showing a magnetized structure of a magnet, and

FIG. 10B is a cross sectional side view showing the magnet, according tothe first embodiment;

FIG. 11 is a partially cross sectional side view showing a rotor withthe magnet, according to the first embodiment;

FIG. 12 is an exploded perspective view showing the rotor and themagnet, according to the first embodiment;

FIG. 13 is a schematic front view showing hall ICs provided to theelectric motor, according to the first embodiment;

FIGS. 14A and 14B are waveform charts showing output signals of A-phase,B-phase, and Z-phase of the electric motor when the rotor rotates,according to the first embodiment;

FIG. 15 is a graph showing a relationship between the rotor angle and anenergizing condition of the coil in a normal operation, according to thefirst embodiment;

FIG. 16 is a graph showing a relationship between the rotor angle and anenergizing condition of the coil, according to a second and thirdembodiments of the present invention; and

FIG. 17 is a graph showing a relationship between the rotor angle and anenergizing condition of the coil, according to an example of anembodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS First Embodiment

As shown in FIGS. 1A to 3, a shift range switching apparatus includes arotative actuator 1 (FIG. 2) that switches a shift range switchingdevice 3, which includes a parking switching device 4 (FIG. 4). Theshift range switching device 3 is an example of a driven object. Theshift range switching device 3 is provided to an automatic transmission2 of a vehicle. The rotative actuator 1 is a servo device that operatesthe shift range switching device 3. The rotative actuator 1 includes asynchronous electric motor 5 and a reduction gear (reduction unit) 6.The reduction gears 6 reduce rotation speed of the electric motor 5. Theelectric motor 5 is controlled using an ECU (electronic control unit) 7.The ECU 7 serves as a motor control unit.

Specifically, the ECU 7 controls the rotative direction of the electricmotor 5, the rotation speed (number of rotation) of the electric motor5, and rotation angle of the electric motor 5 in the shift rangeswitching apparatus, thereby operating the shift range switching device3 via the reduction gears 6.

In the following description, the right side in FIG. 2 is defined as afront side, and the left side in FIG. 2 is defined as a rear side.

Next, the electric motor 5 is described in reference to FIGS. 2, 5. Theelectric motor 5 is a blushless switched reluctance motor (SR motor), inwhich a permanent magnet is not used. The electric motor 5 includes arotor 11 and a stator 12. The rotor 11 is rotatable. The stator 12 isarranged coaxially with respect to the rotation center of the rotor 11.

The rotor 11 is constructed of a rotor shaft 13 and a rotor core 14. Therotor shaft 13 is rotatably supported using a front ball bearing 15 anda rear ball bearing 16. The front ball bearing 15 is provided to a frontend of the rotor shaft 13, and the rear ball bearing 16 is provided to arear end of the rotor shaft 13.

The front ball bearing 15 engages with the inner circumferentialperiphery of an output shaft 17 of the reduction gears 6. The outputshaft 17 of the reduction gears 6 is rotatably supported via a metalbearing 19, which is arranged in the inner circumferential periphery ofthe front housing 18. That is, the front end of the rotor shaft 13 isrotatably supported via the metal bearing 19, the output shaft 17, andthe front ball bearing 15, which are provided in a front housing 18.

The metal bearing 19 supports the front end of the rotor shaft 13 in asupporting range, which axially overlaps a supporting range of the frontball bearing 15. In this structure, the rotor shaft 13 can be restrictedfrom being inclined due to reactive force of the reduction gears 6.Specifically, the reactive force is caused by a load applied to thegearing portion between a sun gear 26 and a ring gear 27. The rear ballbearing 16 is press-inserted into the outer circumferential periphery ofthe rear end of the rotor shaft 13, thereby being supported by a rearhousing 20. The rear housing 20 serves as a stator housing.

The stator 12 is constructed of a fixed stator core 21 and magnetizingcoil (coil device) 22. The coil device 22 generates magnetic force bybeing energized. The coil device 22 is multiphase. Specifically, asshown in FIGS. 5, 6, the coil device 22 has a first coil group 22A and asecond coil group 22B. The first coil group 22A includes coils U1, V1,and W1. The second coil group 22B includes coils U2, V2, and W2. Thecoils U1, V1, and W1 of the first coil group 22A and the coils U2, V2,and W2 of the second coil group 22B construct a multiphase structure ofthe coil device 22.

The stator core 21 is constructed of stacked thin plates. The statorcore 21 is fixed to the rear housing 20 (FIG. 2). As referred to FIG. 5,the stator core 21 has stator teeth 23 (introverted salient poles) thatprotrude inwardly toward the rotor core 14. The stator teeth 23 arearranged at substantially regular circumferential intervals, which aresubstantially 30°. Each of the coils U1, V1, and W1 of the first coilgroup 22A is wound around each of the stator teeth 23 to generatemagnetic force in each of the stator teeth 23. Each of the coils U2, V2,and W2 of the second coil group 22B is wound around each of the statorteeth 23 to generate magnetic force in each of the stator teeth 23. Thecoils U1, U2 are in U-phase, the coils V1, V2 are in V-phase, and thecoils W1, W2 are in W-phase.

Next, the coil device 22 is described in reference to FIGS. 5, 6. Asshown in FIG. 6, the coils U1, V1, and W1 of the first coil group 22Aare wound separately from the coils U2, V2, and W2 of the second coilgroup 22B in the coil device 22. The coils U1, V1, and W1 of the firstcoil group 22A and the coils U2, V2, and W2 of the second coil group 22Bare connected respectively in a manner of the star connection. The rotor11 can be rotated by supplying electricity only to the coils U1, V1, andW1 of the first coil group 22A. Alternatively, the rotor 11 can berotated by supplying electricity only to the coils U2, V2, and W2 of thesecond coil group 22B.

The coils U1, V1, and W1 of the first coil group 22A and the coils U2,V2, and W2 of the second coil group 22B are divided into multiplewindings. In this embodiment, the number of the windings is two.Specifically, the coils U1, V1, and W1 of the first coil group 22A areconstructed of a first group of the coils U1-1, V1-1, and W1-1 and asecond group of the coils U1-2, V1-2, and W1-2. The first group of thecoils U1-1, V1-1, and W1-1 are respectively provided to the stator teeth23, which are in series along the rotative direction. The second groupof the coils U1-2, V1-2, and W1-2 are respectively provided to thestator teeth 23, which are in series along the rotative direction. Thesecond group of the coils U1-2, V1-2, and W1-2 continues from the firstgroup of the coils U1-1, V1-1, and W1-1 along the rotative direction.

The coils U2, V2, and W2 of the second coil group 22B are constructed ofa first group of the coils U2-1, V2-1, and W2-1 and a second group ofthe coils U2-2, V2-2, and W2-2. The first group of the coils U2-1, V2-1,and W2-1 are respectively provided to the stator teeth 23, which are inseries along the rotative direction. The second group of the coils U2-2,V2-2, and W2-2 are respectively provided to the stator teeth 23, whichare in series along the rotative direction. The second group of thecoils U2-2, V2-2, and W2-2 continues from the first group of the coilsU2-1, V2-1, and W2-1 along the rotative direction.

When the coil device 22 is energized, the groups of the coilsrespectively generate magnetism indicating magnetic poles, which areopposite to each other in the rotative direction. Specifically, forexample, when the coil device 22 is energized, and when the inner endsof the first group of the coils U1-1, V1-1, and W1-1 are magnetized inthe north pole, the adjacent inner ends of the second group of the coilsU1-2, V1-2, and W1-2 are magnetized in the south pole, the adjacentinner ends of the first group of the coils U2-1, V2-1, and W2-1 aremagnetized in the north pole, and the adjacent inner ends of the secondgroup of the coils U2-2, V2-2, and W2-2 are magnetized in the southpole.

In this situation, for example, when two coils U1-1, U1-2 are energized,the radially inner portion of the stator tooth 23, around which the coilU1-1 is wound, is magnetized in the north pole, and the radially innerportion of the stator tooth 23, around which the coil U1-2 is wound, ismagnetized in the south pole. The stator tooth 23, around which the coilU1-1 is wound, is disposed substantially 90° distant from the statortooth 23, around which the coil U1-2 is wound, with respect to therotative direction of the stator core 21.

Similarly, in the coils V1, W1, U2, V2, W2, one of two stator teeth 23,which is distant from the other of the two stator teeth 23 forsubstantially 90° in the rotative direction, generates magnetism of oneof the south pole and the north pole. In this case, the other of the twostator teeth 23 generates the other of the south pole and the northpole.

As referred to FIG. 2, the rotor core 14 is constructed by stacking thinplates. The rotor core 14 is press-inserted into and fixed to the rotorshaft 13. The rotor core 14 has rotor teeth 24 (extroverted salientpoles, FIG. 5) that outwardly protrude to the stator core 21 on theradially outer side thereof. The rotor teeth 24 are arranged atsubstantially regular circumferential intervals, which are substantially45°.

The energizing position and the energizing direction of the coil device22 of the U-phase, V-phase, and W-phase are sequentially switched, sothat the stator teeth 23, which magnetically attract the rotor teeth 24,are switched. Thus, the rotor 11 is rotated in both the normal directionand the reverse direction.

Next, the reduction gears 6 are described in reference to FIGS. 7 to 9.

The reduction gears 6 are cycloidal gears, for example. The reductiongears 6 are some type of a planetary gear train, which constructs aninscribed planetary gear reduction mechanism. The reduction gears 6includes a sun gear 26 (inner gear, external gear), a ring gear 27(outer gear, internal gear), and a transmission device 28. The sun gear26 is capable of rotating eccentrically with respect to the rotor shaft13 via an eccentric portion 25, which is provided to the rotor shaft 13.The ring gear 27 internally engages with the sun gear 26. Thetransmission device 28 transmits rotation of the sun gear 26 to theoutput shaft 17.

The eccentric portion 25 is an axis that rotates eccentrically withrespect to the rotation center of the rotor shaft 13, thereby rotatingthe sun gear 26 along an orbital path. The eccentric portion 25rotatably supports the sun gear 26 via a sun gear bearing 31, which isprovided to the circumferential outer periphery of the eccentric portion25.

As described above, the sun gear 26 is rotatably supported via the sungear bearing 31 such that the sun gear 26 is capable of rotating withrespect to the eccentric portion 25 of the rotor shaft 13. As theeccentric portion 25 rotates, The sun gear 26 is rotated in a condition,in which the sun gear 26 is pressed onto the ring gear 27. The ring gear27 is fixed to the front housing 18.

The output shaft 17 rotates integrally with a flange 33. The flange 33is arranged to the rear end of the output shaft 17. The flange 33 hasmultiple inner pin holes 34, which are formed coaxially with the flange33. The sun gear 26 has a front surface, from which multiple inner pins35 protrude. The inner pins 35 of the sun gear 26 loosely engage withthe inner pin holes 34 of the flange 33, so that the transmission device28 is constructed. Thus, rotation of the sun gear 26 is transmitted tothe output shaft 17.

In this structure, the rotor shaft 13 rotates, so that the sun gear 26eccentrically rotates, and the sun gear 26 reduces rotation speed withrespect to the rotation of the rotor shaft 13. The reduced rotationspeed of the sun gear 26 is transmitted to the output shaft 17. Theoutput shaft 17 connects with a control rod 45 (FIG. 4) of the shiftrange switching device 3.

The sun gear 26 may have the multiple inner pin holes 24, and the flange33 may have the multiple inner pins 35, dissimilarly to the abovestructure.

Next, the shift range switching device 3 is described in reference toFIGS. 3, 4.

The shift range switching device 3 including the parking switchingdevice 4 is switched using the output shaft 17 of the reduction gears 6.A manual spool valve 42 provided to a hydraulic valve body 41 is slidand displaced to a predetermined position, so that hydraulic passagesare switched. The hydraulic passages are connected to a hydraulic clutch(not shown) of the automatic transmission 2. Thus, the engagementcondition of the hydraulic clutch is controlled, so that the shiftranges such as P, R, N, and D in the automatic transmission 2 areswitched.

The parking switching device 4 is locked and unlocked by engagement anddisengagement between a recession 43 a of a park gear 43 and aprotrusion 44 a of the park pole 44. The park gear 43 connects with anoutput shaft (not shown) of the automatic transmission 2 via adriveshaft (not shown) and a differential gear (not shown). The parkgear 43 is restricted in rotation thereof, so that the drive wheel ofthe vehicle is locked, consequently the vehicle becomes in the parkingcondition.

The control rod 45 is driven using the reduction gears 6. A detent plate46, which is in a substantially sector form, is connected to the controlrod 45 with a spring pin or the like (not shown). The detent plate 46has multiple recessions 46 a in the radially tip end thereof. Theradially tip end of the detent plate 46 is the arc shaped portion in thesector-shaped portion. A detent spring 47 is fixed to the hydraulicvalve body 41. The detent spring 47 has a hooking portion 47 a in thetip end thereof. The hooking portion 47 a hooks to one of the recessions46 a of the detent plate 46, so that the shift range is maintained.

Both ends of the recessions 46 a of the detent plate 46 between the Prange and the D range have restriction walls. The hooking portion 47 aof the detent spring 47 hooks to the restriction walls, so that therestriction walls restrict the electric motor 5 from rotating.Specifically, the detent plate 46 does not have rigid walls forrestricting electric motor 5 from rotating. The restriction walls areimaginary wall. The hooking portion 47 a of the detent spring 47 hooksto the recession 46 a of the detent plate 46, so that the restrictionwalls restrict the electric motor 5 from further rotating.

The detent plate 46 has a pin 48 that operates the manual spool valve42. The pin 48 engages with a groove 49 that is formed in the end of themanual spool valve 42. When the detent plate 46 is rotated via thecontrol rod 45, the pin 48 is moved along an arch-shaped path, so thatthe manual spool valve 42, which engages with the pin 48, linearly movesin the hydraulic valve body 41.

When the control rod 45 is rotated in the clockwise direction withrespect to the direction when being viewed from the arrow A in FIG. 4,the pin 48 pushes the manual spool valve 42 into the hydraulic valvebody 41 via the detent plate 46. Thus, the hydraulic passages in thehydraulic valve body 41 are switched in the order of D, N, R, and Pranges, so that the shift ranges of the automatic transmission 2 areswitched in the order of D, N, R, and P ranges. When the control rod 45is rotated in the reverse direction, the pin 48 pulls the manual spoolvalve 42 from the hydraulic valve body 41, so that the hydraulicpassages in the hydraulic valve body 41 are switched in the order of P,R, N, and D ranges. Thus, the shift ranges of the automatic transmission2 are switched in the order of P, R, N, and D ranges.

The detent plate 46 is provided with a park rod 51 for operating thepark pole 44. The park rod 51 has a tip end, to which a conical portion52 is provided.

The conical portion 52 is interposed between a protrusion 53 of thehousing of the automatic transmission 2 and the park pole 44. When thecontrol rod 45 is rotated from the R range to the P range in theclockwise direction with respect to the direction when being viewed fromthe arrow A in FIG. 4, the park rod 51 is displaced via the detent plate46 in the direction shown by arrow B in FIG. 4. Thus, the conicalportion 52 raises the park pole 44, so that the park pole 44 rotatesaround a shaft 44 b in the direction shown by the arrow C in FIG. 4.Thus, the protrusion 44 a of the park pole 44 engages with the recession43 a of the park gear 43. In this condition, the parking switchingdevice 4 becomes in a lock condition.

When the control rod 45 is rotated from the P range to the R range inthe counterclockwise direction, the park rod 51 is pulled in thedirection opposite to the arrow B in FIG. 4, so that the conical portion52 terminates raising the park pole 44. The park pole 44 is regularlybiased using a coil spring (not shown) in the direction opposite to thearrow C in FIG. 4, so that the protrusion 44 a of the park pole 44 isdetached from the recession 43 a of the park gear 43. In this condition,the park gear 43 becomes free from the park pole 44, so that the parkingswitching device 4 becomes in the unlock condition.

Next, an encoder 60 is described in reference to FIGS. 2, 10A to 14B.The rotative actuator 1 has the housing, which is constructed of thefront housing 18 and the rear housing 20. The housing of the rotativeactuator 1 accommodates the encoder (rotation angle detecting device) 60that detects the rotation angle of the rotor 11. The electric motor 5can be rotated at high speed while maintaining synchronism, by detectingthe rotation angle of the rotor 11 using the encoder 60.

The encoder 60 is an incremental encoder, which includes a magnet 61 anda hall IC 62. The magnet 61 rotates integrally with the rotor 11. Thehall IC 62 is arranged in the rear housing 20 for detecting magnetism.As shown in FIG. 13, the hall IC 62 includes a first rotation angularhall IC 62A, a second rotation angular hall IC 62B, and an index hall IC62Z. The hall IC 62 is supported by a substrate 63 (FIG. 2) mounted inthe rear housing 20.

As shown in FIGS. 10A to 12, the magnet 61 is in a substantially annulardisc shape, and is arranged coaxially with respect to the rotor shaft13. The magnet 61 connects with the axial end surface in the rear sideof the rotor core 14. When the rotor core 14 exerts large magneticinfluence to the magnet 61, the magnet 61 may be connected with therotor core 14 via a non-magnetic diaphragm (not shown) to reduce theinfluence of the magnetism. When the rotor core 14 exerts small magneticinfluence to the magnet 61, the magnet 61 may be directly connected withthe rotor core 14. In this structure, the number of components can bereduced, so that manufacturing cost can be reduced.

As shown in FIG. 12, the rear surface of the rotor core 14 has multipleholes 14 a for alignment of the magnet 61. The magnet 61 has aconnecting surface, on which multiple protrusions 61 a are provided. Theprotrusions 61 a of the magnet 61 are inserted into the correspondingholes 14 a of the rotor core 14, so that the magnet 61 is assembled tothe rotor core 14 such that the magnet 61 is substantially coaxial withrespect to the rotation center of the rotor core 14.

As shown in FIG. 11, the magnet 61 has the rear end surface, whichopposes to the hall IC 62 (FIG. 2). The rear end surface of the magnet61 is magnetized for detecting the rotation angle and an index for aphase to be energized, thereby generating magnetism in the axialdirection of the magnet 61.

Next, magnetized structure of the rear surface of the magnet 61 isdescribed in reference to FIGS. 10A, 10B.

The magnet 61 has a rotation angular magnetized portion α on the rearsurface thereof on the outer peripheral side thereof. The rotationangular magnetized portion α multipolar magnetized portions along therotative direction thereof for generating rotative angular signals andfor terminating the rotative angular signals. Magnetized index portionsβ and non-magnetized index portions β′ are provided to be adjacent tothe inner periphery of the rotation angular magnetized portion α alongthe rotative direction of the magnet 61. The magnetized index portions βgenerate the index signals and terminate the index signals. Thenon-magnetized index portions β′ do not perform the operation of thegenerating the index signals.

The rotation angular magnetized portion α has multipolar magnetizedportions along the rotative direction thereof for generating rotativeangular signals, which includes A-phase signals and B-phase signals. Inthe structure of the rotation angular magnetized portion a shown in FIG.10A, the portion (north pole portion), which generates the magnetism(north pole magnetism) of the north pole, and the portion (south poleportion), which generates the magnetism (south pole magnetism) of thesouth pole, are alternatively arranged at intervals of substantially7.5°, for example. Specifically, the rotation angular magnetized portionα has 48 poles of A-phase sensing portions and B-phase sensing portions,for example.

The magnetized index portions β respectively generate index signals(Z-phase signal) at intervals of 45°, for example. The coil device 22 ofthe U-phase V-phase, and W-phase make around at the intervals of 45°,for example. Each of the magnetized index portions β includes theportion (north pole portion) magnetized to generate the north polemagnetism for a range of 7.5°. Portions (south pole portion) magnetizedto generate the south pole magnetism are arranged on both sides of thenorth pole portion along the rotative direction, in each of themagnetized index portions β.

Each of the non-magnetized index portions β′ is arranged between twomagnetized index portions β, which are adjacent to each other along therotative direction. Each non-magnetized index portion β′ is notmagnetized, so that the non-magnetized index portion β′ does notgenerate the index signal.

The first and second rotation angular hall ICs 62A, 62B are supported bythe substrate 63 in a condition, in which the first and second rotationangular hall ICs 62A, 62B respectively oppose to the rotation angularmagnetized portion α in the axial direction. The index hall IC 62Z issupported by the substrate 63 in a condition, in which the index hall IC62Z opposes to the magnetized index portions β and non-magnetized indexportions β′ in the axial direction.

The first and second rotation angular hall ICs 62A, 62B are distant fromeach other relatively for substantially 3.75°, for example (forsubstantially 90° in an electric angle, for example, as shown in FIG.14).

Therefore, the A-phase signal and the B-phase signal are distant fromeach other relatively for substantially 3.75°, for example (forsubstantially 90° in an electric angle, for example).

A hall element and an ON-OFF signal generating IC are integrated toconstruct the first and second rotation angular hall ICs 62A, 62B andthe index hall IC 62Z. The hall element generates a signal in accordancewith an amount of magnetic flux passing through the hall element.

When magnetic flux on the side of the north pole applied to the hallelement becomes greater than a threshold, the ON-OFF signal generatingIC turns the rotation angular signals ON. That is, the ON-OFF signalgenerating IC generates the A-phase signal, B-phase signal, and Z-phasesignal. When the magnetic flux, which is on the side of the south poleand is applied to the hall element, becomes greater than a threshold,the ON-OFF signal generating IC, turns the rotation angular signals OFF.That is, the ON-OFF signal generating IC terminates generating theA-phase signal, B-phase signal, and Z-phase signal.

In this embodiment, the hall ICs 62A, 62B, and 62z, in which the hallelements are integrated with ON-OFF signal generating circuits, aredescribed as an example. However, the hall element may be providedindividually from the ON-OFF signal generating circuit. Specifically,the ON-OFF signal generating circuit may be assembled on the substrate63 separately from the hall element. The ON-OFF signal generatingcircuit may be assembled into the ECU 7.

Next, output waveforms of the A-phase signal, B-phase signal, andZ-phase signal generated using the encoder 60 are described in referenceto FIGS. 14A, 14B.

The A-phase signal has a phase difference with respect to the B-phasesignal relatively for substantially 3.75° (for substantially 90° in anelectric angle), for example. In this embodiment, the A-phase signal andthe B-shape signal are output respectively for one period at everyrotation of substantially 15° of the rotor 11, for example.

The Z-phase signal is the index signal that is output once at everyrotation of substantially 45° of the rotor 11, for example. The indexsignal is used for switching energization of the motor. The index signalis an ON signal in this embodiment, for example. The phase ofenergization of the electric motor 5 and a physical relationship of theA-phase with respect to the B-phase can be defined by this Z-phasesignal.

The substrate 63 supports the first and second rotation angular hall ICs62A, 62B, which axially oppose to the rotation angular magnetizedportion α. The substrate 63 supports the index hall IC 62Z, whichaxially oppose to both the magnetized index portions β andnon-magnetized index portions β′. The substrate 63 is accommodated inthe rear housing 20. The substrate 63 is mounted to the lateral surfaceof the coil device 22 on the rear side.

In the above structure, the encoder 60 is mounted in the rotativeactuator 1, so that the rotative actuator 1 can be downsized.Furthermore, the magnet 61 and the hall IC 62 are arranged on the rearside of the rotor core 14, so that the rotative actuator 1 including theencoder 60 can be restricted from being jumboized in the radialdirection of the rotative actuator 1. Thus, mountability of the rotativeactuator 1 can be enhanced.

Next, the ECU 7 is described in reference to FIG. 3.

The ECU 7 controls electricity supplied to the electric motor 5. The ECU7 is a microcomputer including a CPU, a storage medium (memory) 71, aninput circuit, an output circuit, an electric power source, and thelike. The CPU executes control processings and arithmetic processings.The storage medium 71 is such as a ROM, a stand-by RAM, an EEPROM, and aRAM, for storing programs and data.

As shown in FIG. 3, the ECU 7 is electrically connected with devicessuch as a start switch (ignition switch, accessory switch) 72, anin-vehicle battery 73, an indicating device (indicator) 74, a coiloperating device (driver circuit) 75, a vehicular speed sensor 76, and asensor 77. The indicating device 74 indicates information such as ashift range and a condition of the rotative actuator 1. The indicatingdevice 74 may be a visual display device in a normal operation, awarning light, and a warning beep device, for example. The coiloperating device 75 is used for driving the electric motor 5. The sensor77 includes a shift range detecting sensor, which detects the shiftrange set by the driver, a sensor for detecting the position of a brakeswitch, and sensors for detecting other vehicular conditions. A controldevice 78 controls vehicular electric doors such as an electric slidedoor and an electric trunk opener, for example.

The coil operating device 75 is provided individually from the ECU 7 inthe structure shown in FIG. 3. However, the coil operating device 75 maybe accommodated in a casing of the ECU 7.

Next, the coil operating device 75 is described in reference to FIG. 6.

The electric motor 5 includes the first coil group 22A having the coilsU1, V1, and W1 and the second coil group 22B having the coils U2, V2,and W2. The first coil group 22A and the second coil group 22B areelectrically separated from each other. The coils U1, V1, and W1 of thefirst coil group 22A and the coils U2, V2, and W2 of the second coilgroup 22B are respectively connected in a manner of the star connection.

The coil operating device 75 includes a first switching element 79 a anda second switching element 79 b. The first switching element 79 asupplies electricity respectively with the coils U1, V1, and W1 of thefirst coil group 22A. The second switching element 79 b supplieselectricity respectively with the coils U2, V2, and W2 of the secondcoil group 22B. The ECU 7 turns the first and second switching elements79 a, 79 b ON and OFF, so that the condition of energizing the coils U1,V1, W1, U2, V2, and W2 are switched.

As shown in FIG. 15, when the rotor 11 is rotated, the ECU 7 turns thefirst and second switching elements 79 a, 79 b ON and OFF, so that thecoils of the coil device 22 are serially energized to rotate the rotor11 in accordance with the rotation angle of the rotor 11 and correctionterms of delay in magnetization. The rotation angle of the rotor 11 isdetected using the encoder 60. Alternatively, the ECU 7 may turn thefirst and second switching elements 79 a, 79 b ON and OFF in a manner ofan open loop control, so that the coil device 22 may be seriallyenergized to rotate the rotor 11.

The ECU 7 includes various control programs such as a rotor detectingunit 710, a normal control unit 711, a tapping control unit 700, and areference position recognizing unit 701. The rotor detecting unit 710detects rotation speed of the rotor 11, the number of rotation of therotor 11, the rotation angle of the rotor 11, in accordance with theoutput of the encoder 60, specifically, the first and second rotationangular hall ICs 62A, 62B, and the index hall IC 62Z. The normal controlunit 711 controls the electric motor 5 such that the shift rangeposition of a shift range operating unit (not shown), which is operatedby the driver, corresponds to the shift range position detected usingthe ECU 7.

The normal control unit 711 determines control operations of theelectric motor 5 such as the rotative direction of the electric motor 5,the number of rotation of the electric motor 5, and the rotation angleof the electric motor 5. The normal control unit 711 determines thiscontrol operations of the electric motor 5 in accordance with the shiftrange position of the shift range operating unit (not shown), which isoperated by the driver.

The normal control unit 711 controls electricity supplied to the coildevice 22, which has the multiphase structure, in accordance with thedetermination of the control operations of the electric motor 5. Thus,the normal control unit 711 performs a normal control, in which therotative direction, the number of rotation, and the rotation angle ofthe electric motor 5 are controlled. Specifically, when the ECU 7rotates the electric motor 5, the normal control unit 711 performs asynchronized operation, in which the energizing condition of the coildevice 22 having the multiphase structure is switched in accordance witha detection signal such as the rotation angle of the rotor 11 detectedusing the encoder 60. Thus, the normal control unit 711 controls therotative direction, the number of rotation, and the rotation angle ofthe electric motor 5, so that the ECU 7 switches the shift rangeswitching device 3 via the reduction gears 6.

The tapping control unit 700 performs a tapping control in at least oneof the following conditions. For example, every time when the operationis started by turning the start switch 72 ON, when the number ofstarting the operations increases to a predetermined number, when theshift position is unknown in starting the operation, and when apredetermined learning condition is satisfied, the tapping control unit700 performs the tapping control.

The tapping control unit 700 terminates the tapping control in at leastone of the following conditions. For example, when the tapping controlunit 700 performs the tapping control for a predetermined period, when avariation in the rotation angle of the rotor 11 detected using theencoder 60 does not change for a predetermined period, and when thereference position recognizing unit 701 detects the reference position,the tapping control unit 700 terminates the tapping control.

The tapping control unit 700 controls electricity supplied to theelectric motor 5 to make the movable member of the shift range switchingdevice 3 come into contact with a limit position on the other side ofthe movable range. The limit position of the movable range is on theside of the parking position, for example.

In this embodiment, the tapping control unit 700 performs a one sidetapping control, in which the rotor 11 is rotated until the rotor 11makes contact with the limit position on one side such as the side ofthe parking position, for example. Alternatively, the tapping controlunit 700 may perform the one side tapping control to detect thereference position on the one side, subsequently, the rotor 11 may berotated until the rotor 11 makes contact with the limit position on theother side such as the side of the drive position to detect thereference position on the other side. The tapping control unit 700 mayterminate the control after performing both the one side tapping controland the other side taping control.

The reference position recognizing unit 701 performs the tapping controlusing the tapping control unit 700, thereby learning the position, inwhich the rotor 11 stops rotation thereof, as one of the referenceposition (initial position) of the rotor 11 and the reference position(initial position) of the shift range.

Next, an example of a control performed using the ECU 7 is described.The ECU 7 starts this example of the control when the start switch 72 isturned ON, and terminates this example of the control when the controlcondition is changed to a normal control condition, for example. Bothends of the recessions 46 a of the detent plate 46 between the P rangeand D range have the restriction walls. The hooking portion 47 a of thedetent spring 47 hooks to the recession 46 a of the detent plate 46, sothat the restriction walls restrict the electric motor 5 from rotatingfurther the restriction walls.

When the driver turns the start switch 72 ON, the ECU 7 evaluateswhether the storage medium 71 stores information of the shift range whenthe electricity supply is previously terminated. This evaluation is anexample for estimating whether the ECU 7 performs the tapping control.When the ECU 7 makes a positive determination in this evaluation, theECU 7 sets the present shift range at the shift range where theelectricity is previously terminated. Subsequently, the control of theECU 7 proceeds to the normal control, in which the electric motor 5 iscontrolled such that the commanded shift range corresponds to thepresent shift range.

When the present shift range is unknown, that is, the storage medium 71does not store information of the shift range when the electricitysupply is previously terminated, a negative determination is made in theabove evaluation. In this case, the ECU 7 operates the tapping controlunit 700 to perform the tapping control. Specifically, the ECU 7forcibly operates the electric motor 5 until the rotor 11 makes contactwith the limit position on one side of the P range and the D range. TheECU 7 stores the position, in which the electric motor 5 stops rotationthereof on one side of the P range and D range, as the present shiftrange, thereby operating the reference position recognizing unit 701 forstoring the present shift range in the storage medium 71. Subsequently,the routine proceeds to the normal control.

The ECU 7 performs the tapping control, in which the ECU 7 rotates therotor 11 until the rotor 11 makes contact with the limit position on theone side. Accordingly, when the hooking portion 47 a of the detentspring 47 makes contact with the restriction walls on both sides, amechanical load arises due to collision therebetween.

Furthermore, the hooking portion 47 a of the detent spring 47 urges boththe restriction walls of the detent plate 46 due to output torque of theelectric motor 5. As a result, mechanical load torque is applied to thecomponents such as the transmission system of the rotation members andthe hooking portion between the movable member and the fixed member,specifically, the hooking portion 47 a of the detent spring 47, due tothe output torque of the electric motor 5. Accordingly, as the number ofthe tapping control, in which the large load torque is applied,increases, mechanical damage may occur in the components of transmissionsystem and in the hooking portion. As a result, the components of thetransmission system and the hooking portion may be gradually deformedand broken.

However, in the above structure of this embodiment, the electric motor 5includes the first coil group 22A and the second coil group 22B, whichare electrically separated from each other. The first coil group 22A hasthe coils U1, V1, and W1. The second coil group 22B has the coils U2,V2, and W2. The rotor 11 can be rotated by only energizing the coils U1,V1, and W1 of the first coil group 22A or by only energizing the coilsU2, V2, and W2 of the second coil group 22B.

As shown in FIG. 1B, the tapping control unit 700 controls to supplyelectricity only to the coils U1, V1, and W1 of the first coil group 22Afor rotating the rotor 11, when the tapping control unit 700 performsthe tapping control, for example. As a result, torque output from theelectric motor 5 can be reduced in the tapping control compared withtorque output in the normal operation of the electric motor 5.

Thus, the mechanical load, which arises when the hooking portion 47 a ofthe detent spring 47 collides against the one restriction wall of thedetent plate 46 in the taping control, can be reduced.

The rotor 11 stops in the condition where the electric motor 5 issupplied with electricity, specifically, when the hooking portion 47 aof the detent spring 47 collides against the one restriction wall of thedetent plate 46 in the tapping control. In this situation, in the abovestructure, the torque output from the electric motor 5 can be reduced.Therefore, mechanical load torque, which arises in components such asthe hooking portion 47 a of the detent spring 47 in the transmissionsystem and the hooking portion between the movable member and the fixedmember, can be reduced.

In the above structure, when the ECU 7 performs the tapping control, therotor 11 is rotated by energizing only the coils U1, V1, and W1 of thefirst system 22A, for example. Thus, the load due to collision arisingin the tapping control can be reduced. Specifically, load torque arisingin the condition where the hooking portion 47 a of the detent spring 47collides against the one restriction wall of the detent plate 46 can bereduced. Therefore, mechanical damage caused by the tapping control canbe reduced.

In this operation, even when the number of the tapping controlincreases, the components of the transmission system such as the hookingportion 47 a and the hooking portion between the movable member and thefixed member can be steadily restricted from being deformed and damaged.Thus, durability and reliability of the shift range switching device canbe enhanced.

Second Embodiment

The characteristic of the battery (power source), which supplieselectricity to the electric motor 5, may vary in dependence upon theenvironment of the battery. Specifically, output voltage of the batteryand a performance for supplying electricity to the electric motor 5 mayvary in dependence upon the environment such as the season. Inparticular, the variation in the characteristic of the battery is apt tobe large in summer and winter. In these cases, output torque of theelectric motor 5 may vary due to the variation in output voltage of thepower source and the variation in the capacity of the power source forsupplying electricity.

Furthermore, the components are not completely rigid members, and may bedeformed by applying force. That is, the components are macroscopicallyspring elements. Accordingly, when the output torque of the electricmotor 5 varies, an amount of deformation arising in the components inthe tapping control may vary. As a result, the reference positionlearned during the tapping control may not be constant, andconsequently, the variation arising in the tapping control may exert anegative effect to accuracy in the positioning control.

Specifically for example, when voltage applied to the electric motor 5and a capacity of the battery for supplying electricity to the electricmotor 5 increases, output torque of the electric motor 5 may becomelarge. In this condition, when the tapping control is performed, themechanical load becomes large in the tapping control, in which thehooking portion 47 a collides against the restriction wall of the detentplate 46.

Furthermore, load torque becomes large in the condition where thehooking portion 47 a of the detent spring 47 collides against the onerestriction wall of the detent plate 46. As a result, as the number ofthe tapping control increases, the number of applying the large loadtorque increases. Consequently, mechanical damage may occur in thecomponents of the transmission system and in the hooking portion. As aresult, the components of the transmission system and the hookingportion may be gradually deformed and broken.

By contrast, when voltage applied to the electric motor 5 and capacityfor supplying electricity to the electric motor 5 excessively decrease,output torque of the electric motor 5 decreases. In particular, outputtorque of the electric motor 5 may decrease by reducing the outputtorque of the electric motor 5 using a duty control during the tappingcontrol. In this case, the hooking portion 47 a of the detent spring 47may not be capable of getting through the recession 46 a of the detentplate 46 due to lack of output power of the rotative actuator 1.

Furthermore, the components are not completely rigid, and maymacroscopically be spring elements. Accordingly, when the output torqueof the electric motor 5 varies, an amount of deformation arising in thecomponents may vary during the tapping control. As a result, thereference position learned during the tapping control may not beconstant, and consequently, the variation during the tapping control mayexert a negative effect to accuracy in the positioning control.

In this embodiment, a current sensor (not shown) is provided to anelectric circuit for monitoring electric current flowing through theelectric motor 5. As shown in FIG. 16, a duty control is performed forelectricity respectively supplied to the coils U1, V1, W1, U2, V2, andW2 of the coil device 22 at least when the tapping control is performed.In the duty control, electric current (electric current per unit oftime) flowing respectively through the coils U1, V1, W1, U2, V2, and W2of the coil device 22 becomes substantially constant.

That is, the ECU 7 controls a period, in which the first and secondswitching elements 79 a, 79 b are turned ON, in a predetermined period(switching period) in the duty control in accordance with the electriccurrent detected using the electric sensor. Thus, electric currentflowing respectively through the coil device 22 is controlled at asubstantially constant amount. Specifically, as the amount of theelectric current detected using the electric sensor becomes large, theperiod, in which the first and second switching elements 79 a, 79 b areturned ON, is controlled to be short in the predetermined period. Bycontrast, as the amount of the electric current detected using theelectric sensor becomes small, the period, in which the first and secondswitching elements 79 a, 79 b are turned ON, is controlled to be long inthe predetermined period.

The relationship, which is between the electric current detected usingthe electric sensor, and the period, in which the first and secondswitching elements 79 a, 79 b are turned ON, is predetermined anddefined using a data map or an arithmetic expression, for example.

In the above structure and operation, the following effects can beproduced.

First, the electric current flowing through the coils U1, V1, W1, U2,V2, and W2 of the coil device 22 can be controlled at a substantiallyconstant amount, even when voltage applied to the electric motor 5 andcapacity of the battery for supplying electricity to the electric motor5 increase due to variation in the environment and the condition of thevehicle, particularly in summer. Thus, the variation in output torque ofthe electric motor 5 can be reduced.

In this operation, the components such as the hooking portion 47 a inthe transmission system and the hooking portion between the movablemember and the fixed member can be steadily restricted from beingdeformed and damaged during the tapping control due to increase in theoutput power of the electric motor 5 in dependence upon the environmentand condition of the vehicle. Thus, durability and reliability of theshift range switching device can be enhanced.

Second, the electric current flowing through the coils U1, V1, W1, U2,V2, and W2 of the coil device 22 is controlled at a substantiallyconstant amount, even when voltage applied to the electric motor 5 andthe capacity of the battery for supplying electricity to the electricmotor 5 decrease due to environment such as mid-winter and due toincrease in electric resistance in the electric circuit. As a result,output torque of the electric motor 5 can be restricted from decreasingdue to the environment and the condition of the vehicle. For example,even when the output torque of the electric motor 5 is reduced using theduty control or the like during the tapping control, the output torqueof the electric motor 5 can be maintained to be greater than apredetermined amount. Therefore, the hooking portion 47 a of the detentspring 47 can get through the recession 46 a of the detent plate 46, sothat durability and reliability of the shift range switching device canbe enhanced.

Furthermore, when the tapping control is performed, the variation in theoutput torque of the electric motor 5 can be reduced, so that thevariation in the reference position, which is learned during the tappingcontrol, can be reduced. Thus, accuracy in the positioning control canbe enhanced.

A voltage sensor may be provided in the electric circuit, instead of thecurrent sensor, for detecting voltage of electricity supplied to theelectric motor 5. Battery voltage may be used as the voltage of theelectricity supplied to the electric motor 5. The duty ratio ofelectricity supplied to the magnetic coils 22 can be controlled inaccordance with the voltage detected using the voltage sensor.

Third Embodiment

As the rotation speed of the electric motor 5 increases, the outputtorque of the electric motor 5 is apt to decrease. By contrast, as therotation speed of the electric motor 5 decreases, the output torque ofthe electric motor 5 is apt to increase. Therefore, the electric motor 5generates substantially the maximum torque when the electric motor 5stops. That is, when the hooking portion 47 a of the detent spring 47collides against the restriction wall of the detent plate 46, and theelectric motor 5 stops during the tapping control, the electric motor 5generates substantially the maximum torque.

Accordingly, as the number of the tapping control increases, mechanicaldamage may occur in the components of transmission system and in thehooking portion. As a result, the components of the transmission systemand the hooking portion may be gradually deformed and broken.

Furthermore, the components are not completely rigid, and maymacroscopically be spring elements. Accordingly, when the output torqueof the electric motor 5 varies, an amount of deformation arising in thecomponents may vary during the tapping control. As a result, thereference position learned during the tapping control may not beconstant, and consequently, the variation during the tapping control mayexert a negative effect to accuracy of the positioning control.

In this embodiment, as referred to FIG. 16, a duty control is performedfor electricity respectively supplied to the coils U1, V1, W1, U2, V2,and W2 of the coil device 22 in accordance with the rotation speed ofthe rotor 11 at least when the tapping control is performed. Therotation speed of the rotor 11 is detected using the encoder 60. In theduty control, the output torque of the rotor 11 becomes substantiallyconstant.

That is, the ECU 7 controls the period, in which the first and secondswitching elements 79 a, 79 b are turned ON, in the predetermined period(switching period) in the duty control in accordance with the rotationspeed of the rotor 11. Thus, the output torque of the rotor 11 iscontrolled at a substantially constant amount. Specifically, as therotation speed of the rotor 11 becomes high, the period, in which thefirst and second switching elements 79 a, 79 b are turned ON, iscontrolled to be long in the predetermined period. By contrast, as therotation speed of the rotor 11 becomes low, the period, in which thefirst and second switching elements 79 a, 79 b are turned ON, iscontrolled to be short in the predetermined period.

The relationship between the rotation speed of the rotor 11 and theperiod, in which the first and second switching elements 79 a, 79 b areturned ON, is predetermined and defined using a data map or anarithmetic expression, for example.

In the above structure and operation, the following effects can beproduced.

First, as the rotation speed of the rotor 11 becomes high, the amount ofelectricity supplied to the coil device 22 is increased, and as therotation speed of the rotor 11 becomes low, the amount of electricitysupplied to the coil device 22 is decreased, such that the output torqueof the rotor 11 becomes substantially constant. Thus, the output torqueof the electric motor 5 can be restricted when the electric motor 5 isstopped in the condition where the electric motor 5 is supplied withelectricity.

As a result, the output torque of the electric motor 5 can be restrictedin the condition where the hooking portion 47 a of the detent spring 47collides against the restriction wall of the detent plate 47 during thetapping control. Thus, the components such as the hooking portion 47 ain the transmission system and the hooking portion between the movablemember and the fixed member can be steadily restricted from beingapplied with mechanical load torque.

In this operation, even when the number of the tapping controlincreases, the components of the transmission system such as the hookingportion 47 a and the hooking portion between the movable member and thefixed member can be steadily restricted from being deformed and damaged.Thus, durability and reliability of the shift range switching device canbe enhanced.

Furthermore, the variation in the output torque of the electric motor 5can be reduced during the tapping control, so that the variation in thereference position, which is learned during the tapping control, can bereduced. Thus, accuracy in the positioning control can be enhanced.

[Variation]

The first embodiment can be combined with the second embodiment.Specifically, as shown in FIG. 17, when the tapping control isperformed, only the coils U1, V1, and W1 of the first coil group 22A maybe supplied with electricity, so that the output torque of the electricmotor 5 is reduced. In addition, the duty control may be performed tothe electricity respectively supplied to the coil device 22 such thatthe amount of electricity respectively flowing through the coil device22 becomes substantially constant.

The first embodiment can be combined with the third embodiment.Specifically, when the tapping control is performed, only the coils U1,V1, and W1 of the first coil group 22A may be supplied with electricity,so that the output torque of the electric motor 5 is reduced. Inaddition, a duty control may be performed to the electricityrespectively supplied to the coil device 22 such that the output torqueof the rotor 11 becomes substantially constant.

The second embodiment can be combined with the third embodiment.Specifically, when the tapping control is performed, the duty controlmay be performed to the electricity respectively supplied to the coildevice 22 such that the amount of electricity respectively flowingthrough the coil device 22 becomes substantially constant. In addition,the duty control may be performed to the electricity respectivelysupplied to the coil device 22 such that the output torque of the rotor11 becomes substantially constant.

The first, second, and third embodiments can be combined with eachother. Specifically, when the tapping control is performed, only thecoils U1, V1, and W1 of the first coil group 22A may be supplied withelectricity, so that the output torque of the electric motor 5 isreduced. In addition, the duty control may be performed to theelectricity respectively supplied to the coil device 22 such that theamount of electricity respectively flowing through the coil device 22becomes substantially constant. In addition, the duty control may beperformed to the electricity respectively supplied to the coil device 22such that the output torque of the rotor 11 becomes substantiallyconstant.

The encoder 60 may be omitted. In this structure, the number ofsupplying electricity respectively to the coil device 22 may be counted,so that the number of rotation of the rotor 11 and the rotation speed ofthe rotor 11 may be controlled.

The present shift range may be detected using an angular sensor fordetecting the angle of the output shaft 17 of the reduction gears 6,instead of detecting the present shift range in accordance with thenumber of rotation of the rotor 11 and the rotation angle of the rotor11. In this case, abnormality in the angular sensor can be detected byperforming the tapping control.

The electric motor 5 is not limited to the SR motor. Other kinds ofreluctance motor such as a synchronous reluctance motor may be used.Other kind of synchronous motor such as a surface permanent magnet (SPM)synchronous motor, and an interior permanent magnet (IPM) synchronousmotor may be used. Alternatively, various kinds of motors may be used asthe electric motor 5.

The reduction gears 6 are not limited to the inscribed planetaryreduction gear (cycloidal gears). A planetary reduction gear constructedof the sun gear 26, planetary pinions, a ring gear, and the like may beused as the reduction gears 6. The sun gear 26 is rotated by the rotorshaft 13. The planetary pinions are arranged along the circumferentialperiphery of the sun gear 26 at regular intervals. The ring gear engageswith the circumferential periphery of the planetary pinion.

The reduction gears 6 may be constructed of the sun gear 26 and a geartrain. The gear trains engage with the sun gear 26.

The rotative actuator 1 is not limited to operate the shift rangeswitching device 3, which is an example of the driven object. Therotative actuator 1 may operate other driven object such as a cam phasevariable device, which variably changes the advanced phase of thecamshaft.

The electric motor 5 is not limited to be combined with the reductiongears 6. The electric motor 5 may directly operate a driven object.

The structure of the above embodiment is an example. Specifically, theangular dimensions and arrangement of the components such as the magnetand the hall ICs may be variously changed.

The above detecting apparatus is not limited for detecting the referenceposition. The structure of the above detecting apparatus can be appliedto various detecting apparatus, which manipulate a member until themember makes contact with an object for detecting a position of one ofthe member and the object, while mechanical load is reduced between themember and the object, for example.

It should be appreciated that while the processes of the embodiments ofthe present invention have been described herein as including a specificsequence of steps, further alternative embodiments including variousother sequences of these steps and/or additional steps not disclosedherein are intended to be within the steps of the present invention.

Various modifications and alternations may be diversely made to theabove embodiments without departing from the spirit of the presentinvention.

1. A reference position detecting apparatus comprising: an electricmotor that includes a coil device and a rotor, the rotor rotating whenthe coil device is supplied with electricity; a driven object that isdriven by the rotating rotor; a tapping control unit that performs atapping control, in which the rotor rotates to a limit position on oneside in a movable range of the driven object; and a reference positionrecognizing unit that defines a point, at which rotation of the rotorstops, as a reference position of one of the rotor and the driven objectduring the tapping control, wherein the coil device has a first coilgroup and a second coil group, the first coil group includes a pluralityof first coils, which electrically connect with each other, the secondcoil group includes a plurality of second coils, which electricallyconnect with each other, the first coil group including the plurality offirst coils is electrically separated from the second coil groupincluding the plurality of second coils, and the tapping control unitcontrols electricity supplied to either one of the first coil group andthe second coil group to rotate the rotor during the tapping control. 2.The apparatus according to claim 1, wherein the tapping control unitperforms a duty control with respect to electricity supplied to theeither one of the first coil group and the second coil group such thatan amount of electricity flowing through the either one of the firstcoil group and the second coil group becomes substantially constantduring the tapping control.
 3. The apparatus according to claim 1,wherein the tapping control unit performs a duty control with respect toelectricity supplied to the either one of the first coil group and thesecond coil group in accordance with speed of the rotor such that outputtorque of the rotor becomes substantially constant during the tappingcontrol.
 4. The apparatus according to claim 1, wherein the drivenobject is a shift range switching device that is provided to anautomatic transmission for a vehicle, and the electric motor drives theshift range switching device via a reduction unit that reduces outputpower of the electric motor.
 5. The apparatus according to claim 1,wherein the electric motor includes a stator that has a stator corehaving a plurality of stator teeth arranged along a substantiallycircumferential direction of the stator core, the plurality of statorteeth inwardly protruding substantially in a radial direction of thestator core, the plurality of first coils are provided to the pluralityof stator teeth to generate magnetic force in the plurality of statorteeth, the plurality of second coils are provided to the plurality ofstator teeth to generate magnetic force in the plurality of statorteeth, the rotor rotates when at least one of the first coil group andthe second coil group generates magnetic force in the stator teeth, theapparatus further comprising: a motor control unit that switcheselectricity supplied to the plurality of first coils and the pluralityof second coils.
 6. The apparatus according to claim 5, wherein theplurality of first coils includes a coil of U1-phase, a coil ofV1-phase, and a coil of W1-phase, which are respectively provided to theplurality of stator teeth, and the plurality of second coils includes acoil of U2-phase, a coil of V2-phase, and a coil of W2-phase, which areprovided to the plurality of stator teeth.
 7. The apparatus according toclaim 5, further comprising: a stator housing that supports the statorof the electric motor.
 8. The apparatus according to claim 1, whereinthe electric motor is either one of a reluctance motor and a permanentmagnet synchronous motor.